This invention relates to vehicle navigation systems.
It is desirable in many vehicles to be aware of current position as signified on a map to the best attainable degree of accuracy. In most systems, and in particular in aircraft, it is also desirable to be able to measure some if not all current values of orthogonal motion and orientation.
Preferably, current position and orientation measures are derived without reliance on cooperative external agencies such as navigation beacons. Independence of such agencies frees the vehicles from the risk of performance degradation in the event of accidental interruption or deliberate damage or distortion of their services.
Preferably, the means of measurement employed by any such vehicular navigation or orientation system is passive in respect of the non-emission of signals which would be detectable beyond the vehicle. Many such systems would thence be able to work in close proximity without interference or limits on numbers. In military operations, such systems would also be able to navigate without risk of detection.
It is known for manned vehicles to carry maps whereby crewmen may, by visual observation, judge current position. It is also known for both manned and unmanned vehicles to carry inertial navigation systems where current position may be derived by performing mathematics on the aggregation of all accelerations experienced since a last position known by some other means. Such inertial navigation systems, however, inexorably accumulate an unquantifiable positional error over time.
The inertial reference elements of such systems are also known to provide a measure of the vehicles' current orientation by comparison with a known reference, which may be pendular for vertical orientation and a magnetic compass for direction.
It is known for some vehicles to carry stellar navigation systems wherein, by multiple telescopic detections of stars and by reference to an atlas of their immutable apparent relative positions, the orientation of the vehicle in space can be computed. Measurement of the instantaneous local Earth's vertical in the stellar sphere, combined with knowledge of the Earth's rotation rate within that sphere then enables identification of the position of that local vertical on a map to within the accuracy of the measurement devices employed. Such systems are constrained by being only useable when starlight is not obscured and hence, if uninterruptible availability is required, tend to be employed only on high-altitude airborne vehicles or missiles.
It is also known for aircraft to employ active ranging devices, such as radars, to accumulate data on the ground over which they are passing and automatically to compare this data with the pre-stored terrain maps of the ground surface in search of that best-fit mathematical correlation which probabilistically describes their present position.
It is also known for computerized image processing systems receiving serial digitized inputs of matrix detections from imaging sensors to identify automatically objects viewed by the sensor, such as in GB 2206270A. The input information may be one or more frames of video imagery, digitized or otherwise. The information characterizing the object sought is assumed embedded in the serial input data and may be recognized by computational processing with reference to a digital library of such characterizing information.
It is also known that, where the angle subtended by the image of an object so recognized is measurable, and where the real size of that object perpendicular to the direction of viewing is also known by virtue of prior information, then its range or distance from the viewing sensor may be directly calculated, see GB 2228642A.